In recent years, in a vehicle such as an automobile, a head-up display (HUD) device is incorporated in an instrument panel (e.g. Patent Literature 1). An HUD device projects information (image) beneficial to a driver onto a combiner disposed in a viewing direction of a driver or onto a front widow itself when the driver drives a vehicle. The projected image is reflected on the front window, and a virtual image is formed. The driver visually recognizes the virtual image while overlapping the virtual image on a landscape in front of the vehicle.
When a variety of pieces of information are projected on a front window, a projection range of light beam by an HUD device naturally extends. It is necessary to make an optical path length long from a projection light source to a front window in order to form a projection image having a large display size. An instrument panel and a front window are disposed in proximity to each other, and a sufficient optical path length may not be secured between the instrument panel and the front window. In view of the above, it is necessary to secure an optical path length by disposing a mirror for reflecting a projected light beam within a housing of an HUD device, for example. Consequently, the HUD device tends to be a unit of a large size and a heavy weight.
In an HUD device having a large size and a heavy weight as described above, it is necessary to provide a fixing structure having rigidity with respect to a vehicle so that the HUD device is not shaken by vibration applied thereto when a vehicle travels, in other words, a projected image is not shaken. On the other hand, it is desirable to configure the HUD device in such a manner that the HUD device is mountable and dismountable to and from an instrument panel relatively easily for maintenance, repair, and the like of the HUD device.